I just DP'd mine (92 300D) last night, and it was darn near black about halfway through the bottle! I might run a second bottle through just for good measure! Power off idle *seems* better, and I feel better knowing all that mess that blackened the DP is cleaned out of the system. I do plan to change my oil very shortly, though.

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1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)